Clinical Validation

GEP test validated as highly accurate predictor of risk

DecisionDx-Melanoma™ was clinically validated in a prospectively designed, multi-center study using archival tissue samples. Data presented at the 2013 meeting of the American Society of Clinical Oncology showed that the new molecular test is more accurate than current histologic factors used to predict an individual patient’s metastatic risk, including AJCC stage, Breslow’s thickness and mitotic rate.

Castle Biosciences, which discovered and developed the assay, analyzed over 300 cutaneous melanoma (CM) samples obtained from seven centers in the U.S. RNA was isolated from formalin-fixed, paraffin-embedded (FFPE) biopsies or wide local excisions of primary CM from patients with Stage I-IV (82% were Stage I or II) converted to cDNA and analyzed using RT-PCR. The training set was comprised of 164 samples. Independent validation was performed on an additional 104 CM samples.

Using a pre-specified predictive algorithm, the gene expression profile (GEP) signature of a cutaneous melanoma tumor analyzed with the DecisionDx-Melanoma assay was compared to the expression pattern of the training set of patients with known outcomes.

Analysis of the training set showed a sensitivity of predicting metastatic disease of 85% with an area under the Receiver Operating Characteristic (ROC) curve of 91%. Prediction of metastatic risk for the independent validation set resulted in a sensitivity of predicting metastatic disease of 89% and an ROC of 91%. (Table 2).

Independence of the DecisionDx-Melanoma test was evaluated using Cox regression analysis for patients with Stage I or II melanoma. Cox regression analysis was performed using both the individual AJCC staging criteria of Breslow’s thickness, ulceration, and mitosis as well as the combined factors of AJCC stage. The analysis showed that Breslow’s thickness is an important predictor of metastatic disease as is AJCC stage. The DecisionDx-Melanoma test was also shown to be an important predictor of metastasis.

Importantly, multivariate analyses found the DecisionDx-Melanoma test to be superior to and independent of Breslow’s thickness, ulceration status and mitotic index in predicting metastatic disease.

Similarly, multivariate analyses found the DecisionDx-Melanoma test to be superior to and independent of AJCC stage (Stage I, IIA vs IIB, IIC) in predicting metastatic disease in an individual patient.